The entire hutch.. Empty the whole thing, then first clean it with a waterhose, then with soap and then hose it again.. Probably once a month.. Although it depends on the weather, if I'd do this now, the water would freeze and although it would look funny, I don't won't them having to iceskate through their hutch..
But I clean the littertrays (they have two, a big one for cats and a smaller one for rabbits) every other day and I clean the what you call it? The part of the hutch they're supposed to sleep in but never do :lol: well that thing I clean out once a week, put new straw in it etc. Also I sweep the whole hutch when I clean the littertrays.